Fluid catalytic cracking using catalysts containing an alumina-on-silica component

ABSTRACT

Disclosed is a fluid catalytic cracking process using a catalyst composite comprised of an alumina-on-silica material, an inorganic refractory oxide, and optionally a zeolite material. The alumina-on-silica material is comprised of silica particles with surface bound aluminum groups chemically bonded to the silica surface through surface oxygen atoms, which material is dispersed in a matrix of a refractory oxide.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation-in-Part application of U.S. Ser. No. 288,898,filed Dec. 23, 1988, now abandoned, which is a Continuation-in-Partapplication of U.S. Ser. No. 114,835, filed Oct. 30, 1987 and abandonedon Nov. 38, 1989.

FIELD OF THE INVENTION

Fluid catalytic cracking (FCC) is one of the most widely used refineryprocesses for converting heavy oils into more valuable gasoline andlighter products. Wherever there is a rapidly growing demand forgasoline, FCC is the cheapest and fastest route to obtain this premiumpriced product. Consequently, much work has been done through the yearsto improve the yield and/or octane rating of the FCC product slate.Paramount in improving the FCC yield and product slate are the crackingcatalysts employed. While commercial cracking catalysts includeacid-treated natural aluminosilicates, amorphous syntheticsilica-alumina combinations, and crystalline synthetic silica-alumina(zeolites), the most widely used commercial fluid catalytic crackingcatalysts are the zeolites. While zeolites for FCC have met with a veryhigh degree of success, they are nevertheless limited by theirrespective pore sizes as to which hydrocarbon molecules can reach theactive acid sites, the 7.4 Angstrom pore mount of Y-faujasite beingtypical of the upper end of this pore size restriction. Furthermore,there is a tie between a zeolite of a particular structure and thealuminum content range of that zeolite. In certain limited cases, it isnot possible to obtain a particular aluminum content in a specificzeolite structure. Each where this is not the case, it is not uncommonthat one must employ chemical dealumination schemes subsequent tosynthesis to obtain the specific aluminum content or other property thatone desires. As a result, considerable effort has been expended todevelop catalysts comprising either a naturally occurring or syntheticzeolite having, firstly, the desires cracking activity; secondly, poresizes which will permit access to the acid sites of those hydrocarbonmolecules sought to be cracked, and; thirdly, an expanded aluminumcontent range. To date, research has been unable to increase pore sizesbeyond the 7-8 Angstrom range, and inroads into expanding the aluminumcontent range have been limited.

Generally, catalysts of this type are used in compositions frequentlycontaining an "inert" matrix which will reduce cracking activity to acontrolled level and which produces useful products; e.g.,transportation fuels from the FCC process. Catalyst compositions of thistype are taught in U.S. Pat. No. 4,289,606 and the patents and otherreferences therein cited.

A further limitation is encountered in the use of composite catalysts inthe aforementioned FCC process relating to by-product coke deposited onthe catalyst. The catalyst becomes deactivated by the deposition ofcoke, and must be reactivated by burning the coke off the catalyst. Theheat produced by burning is useful in that this is used to bring thefeed to process temperature, and it counteracts the innateendothermicity of cracking reactions. However, it is generally the casethat more coke is produced than is needed to heat balance the process,and since heat balance is the controlling parameter, catalyst isnecessarily recycled in a partially deactivated form; i.e., containingresidual coke. This situation is exacerbated by the progressivelyheavier nature of today's FCC feeds which are prone to making higherlevels of coke. Thus, the need for a catalyst which makes less coke isclear. In addition, there is the need for catalysts which are morestable to the harsh conditions found in the regenerator (600° C-800° C.under steam partial pressure). The steam changes the catalyst in anumber of ways, perhaps the most important of which is to removealuminum from the zeolite, thereby deactivating the zeolite by reducingthe number of acid sites. Manifestly, there is also a need for catalystswith higher steam stability.

More recently, it has been discovered that synthetic, amorphoussilica-alumina compounds, having the capability to catalyze conversionof oxygen-containing hydrocarbons, such as methanol to aromatichydrocarbons such as toluene, can be prepared. Such a catalystcomposition is taught in published U.K. Application No. 2,132,585A. Thisparticular catalyst does not, however, exhibit significant crackingactivity. Even more recently, it has also been discovered that thenumber of acidic sites in a crystalline silica-alumina catalyst, such asa synthetic zeolite, can be increased by coating the zeolite withalumina. Catalysts of this type are taught in published European PatentApplication No. 0,184,305. Such catalysts, however, do not afford anopportunity to control cracking activity over a broad range of acidsites since the minimum activity is controlled by the activity of thezeolite initially selected. Furthermore, the maximum activity is quicklyreached as the importance of the number of sites becomes outweighed bythe lower activity of each site which results from closer siteproximity. Moreover, the cracking activity of catalyst of the typetaught in European Patent Application 0,184,305 is, to a large extent,controlled by the relatively small pore size of the ASM- 5 zeoliteinitially selected for coating with alumina.

From the foregoing, and as is believed well known in the prior art,synthetic zeolite catalysts in composite with inert matrices have acontrolled activity level that produces the desired product slate(s) inconventional commercial processes, but they suffer four drawbacks.Firstly, they are restricted as to the molecular weight of hydrocarboncompounds which can be cracked owing to the pore size thereof. Secondly,there are crystalline constraints on elemental composition; i.e., thealuminum content range which is available with a zeolite of a specificstructure is limited, and a specific aluminum content can sometimes beachieved only subsequent to synthesis by a separate chemicaldealumination step. Thirdly, incompletely regenerated catalysts mustnecessarily be recycled in processes such as FCC because the amount ofcoke made exceeds that which is needed to heat balance the process.Fourthly, zeolites are subject to structural degradation by reactionwith high temperature steam which is a by-product of regeneration.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a fluidcatalytic cracking process which comprises contacting, at fluidcatalytic cracking conditions, a hydrocarbonaceous feed with a catalystcomposite comprised of an alumina-on-silica material dispersed in amatrix material. The alumina-on-silica material is comprised of silicaparticles with surface bound aluminum groups chemically bonded to thesilica surface through surface oxygen atoms, which material is dispersedin a matrix comprised of a refractory oxide, and wherein said materialis prepared by: (i) coating silica particles with an aluminum compoundcapable of being thermally converted to an alumina surface phase underthe conditions of (ii) and (iii) hereof; (ii) treating the coated silicamaterial of (i) to a heat soak at a temperature from about 90° C. toabout 300° C. for an effective amount of time; and (iii) calcining thealuminum coated silica material to form an alumina bound surface phase.

In a preferred embodiment, the silica of the alumina-on-silica materialhas a primary particle size within the range from about 10 Angstroms toabout 1000 Angstroms, a maximum aggregate dimension in any directionwithin the range of about 0.01 microns to about 100 microns and asurface area within the range from about 1 m² /g to about 2000 m² /g,and wherein the material is calcined at a temperature from about 300° C.to about 1000° C.

In another preferred embodiments of the present invention, the silica ofthe alumina-on-silica material is a fumed silica or silica gel; thematrix material is selected from silica, alumina, and silica-aluminasuch that the weight percent of alumina-on-silica to matrix is about 10to 90; and the fluid catalytic cracking conditions in a temperature fromabout 750° F. to about 1300° F. and a pressure from about 0 to 45 psig.

In other preferred embodiments of the present invention, a zeolitematerial, preferably a faujasite, is also present in the composite.

DETAILED DESCRIPTION OF THE INVENTION

As indicated supra, the present invention relates to a fluid catalyticcracking process utilizing an improved catalyst composite comprised ofan alumina-on-silica additive material, a matrix material, andoptionally a zeolite material. The alumina-on-silica material isprepared by coating silica with a suitable aluminum compound andthereafter converting the aluminum compound to a surface bound aluminaphase. The acid activity of this alumina phase may be controlled bycontrolling the temperature at which the catalyst is ultimately calcinedas well as adjusting the aluminum content relative to the surface area.

In general, the alumina-on-silica material of this invention, which isamorphous, may be prepared with essentially any form of silica having amaximum dimension in any direction from about 10 to about 1,000,000Angstroms (100 micrometers), preferably from about 10 to about 100Angstroms, and a surface area within the range from about 1 to about2000 m² g, preferably from about 90 to about 1000 m² /g. Suitablesilicas for use in the alumina-on-silica material include fumed silicas,precipitated silicas, various silica gels, and colloidal silicas. Thealumina-on-silica material will, however, be mast active, without regardto molecular size, when the same is prepared with a relatively smallparticle size silica containing mainly external surface area or internalsurface area in large pores. For this reason, then, preparation with afumed silica and/or silica gel is preferred.

As previously mentioned, the alumina-on-silica component is prepared bycoating the silica with an aluminum compound and thereafter convertingthe aluminum compound to an alumina surface phase. As a result of theconversion, the alumina will become bonded to the silica through oxygenatoms thereby leaving aluminum bearing a formal negative charge on thesurface of the silica. Conversion of the aluminum compound to a surfacebound alumina phase is, then, accomplished such that these negativecharges are balanced with hydrogen cations to create acid sites on thesurface of the alumina-on-silica material. Since the acidic sites are onthe surface of the silica, these sites will be readily accessible to anyfeedstock sought to be converted therewith.

In general, any aluminum compound that can be thermally converted to analumina surface phase such that hydrogen cations are at least thepredominant ion balancing the negative charge created by the reaction ofthe aluminum compound with the silica may be used to coat the silica inpreparing the catalyst of this invention. Suitable aluminum compounds,organoaluminum compounds, and complexes, as well as inorganic aluminumcompounds may be used. In general, the suitable aluminum compounds maybe coated onto the silica either from solution, or in a liquid form suchas in a molten form. In general, the organoaluminum compounds andcomplexes will, when heated to modest temperatures, attach to the silicasurface, and, when heated to a calcining temperature, decompose to forma surface bound alumina phase in such a way that hydrogen cations arethe predominant ion balancing the negative charge on aluminum caused bythe reaction. High melting inorganic aluminum compounds, on the otherhand, must generally be converted to a surface bound alumina phase viahydrothermoconversion to insure contact between the aluminum compoundand the silica surface.

Further, low melting inorganic aluminum compounds will, generally, beconverted to a surface bound alumina phase by hydrothermo-conversion,or, when heated to modest temperatures in physical admixture with thesilica, attach to the silica surface and, when heated to calciningtemperatures, decompose to form a surface bound alumina phase in such away that hydrogen cations are the predominant ion balancing the negativecharge on aluminum caused by the reaction.

Suitable organoaluminum complexes useful in preparation of the catalystof this invention include those in which aluminum is coordinated to anoxygen atom of a chelating agent, such as acetyl acetone,dipivaloylmethane, and ethylene diammine tetraacetic acid, or to anoxygen atom and a heteroatom, such as 8-hydorxyquinoline. Other suitableorganoaluminum complexes are described in Kirk-Othemer, ENCYCLOPEDIA OFCHEMICAL TECHNOLOGY, John Wiley and Sons, Wiley-IntersciencePublication, Vol. 5, pp. 339-367 (1979, Third Edition). Suitableorganoaluminum compounds include aluminum alkoxides, particularlyaluminum alkoxides containing from 1 to about 18 carbon atoms, such asaluminum isopropoxide, aluminum s-butoxide and the like, and aluminumcarboxylates, particularly aluminum carboxylates having from 1 to about18 carbon atoms, such as aluminum butyrate, aluminum decanoate, aluminumstearate and the like. Suitable high melting inorganic aluminumcompounds include aluminum sulfate, aluminum chlorhydrate, and colloidalalumina. Suitable low melting inorganic aluminum compounds includealuminum nitrate and aluminum halides (except for aluminum fluoride).

As indicated supra, the aluminum compound may be coated onto the silicaeither from solution or as a liquid such as in a molten phase. When anorganoaluminum compound is employed, any organic solvent in which theorganoaluminum compound will dissolve may be used. An organic solvent,as opposed to water, is used so as to avoid hydrolysis of theorganoaluminum compound to an inorganic alumina precipitate which willnot readily attach to the silica surface. Suitable organic solventsinclude alkanes such as hexane, heptane, octane and the like; alcoholssuch as propanol, isopropanol, butanol and the like; and aromatichydrocarbons such as benzene, toluene, xylenes, cumene and the like. Ingeneral, and when a solvent is used, the aluminum compound will bedissolved in the solvent in an amount sufficient to provide from about0.1 grams to about 15 grams of aluminum per liter of solvent. As isbelieved readily apparent, the amount of aluminum actually depositedonto the silica can be controlled by controlling the amount of aluminumin solution and the amount of solution actually used since aftercontacting the silica with the aluminum containing solution the solventwill, simply, be evaporated, depositing the aluminum compound onto thesilica. When the aluminum compound is coated onto the silica from aliquid or molten phase, the amount of aluminum actually deposited on thesilica will be controlled by controlling the amount of aluminum compoundactually combined with the silica. When application from the moltenphase is used, however, care should be exercised to avoid prematureconversion of the aluminum compound to an alumina phase before aluminumattachment to the surface has occurred.

In general, coating of the silica with the aluminum compound will becontrolled so as to provide from about 0.0025 mg to about 0.5 mg ofaluminum per square meter of surface area of the silica. The thus coatedsilica will, generally, contain from about 0.01 wt. % to about 20 wt. %aluminum, preferably 1 to 12 wt. % aluminum, and more preferably 2 to 8wt. % aluminum. Coating of the silica with the aluminum compound will beaccomplished at a temperature within the range from about ambienttemperature to about 400° C. and at a pressure within the range fromabout 0.1 mmHg to about 250 atmospheres.

When a solvent is used to deposit the aluminum compound onto the silica,the solvent will be distilled off and recovered for reuse. Again, careshould be exercised in the selection of a solvent to insure that thesolvent can be flashed, or distilled off, at temperatures below thetemperature at which sublimation, or evaporation, of the aluminumcompound will occur. Generally, solvents will be selected which can beflashed or distilled off at a temperature within the range from about-75° C. to about 200° C.

After the solvent has been flashed or distilled off, or after thealuminum compound has been deposited has been deposited on the silica,when a solvent is not used, the next step in the alumina-on-silicapreparation is a mild heat soak at temperatures within the range ofabout 50° C. to about 300° C., preferably from about 75° C. to about250° C., and more preferably from about 100° C. to 200° C., for a timewithin the range from about 1 to about 24 hours, to ensure completeattachment of the aluminum compound to the silica surface. The materialis then calcined at a temperature within the range from about 300° C. toabout 1000° C. When the alumina-on-silica material is calcined at lowertemperatures within this range, the acid sites will be predominantly ofthe Bronsted acid type. When calcined at higher temperatures within thisrange, the acid sites will be predominantly of the Lewis type. Atintermediate temperatures within this range, the acid sites will be amixture of Bronsted and Lewis types. During calcination, the aluminumcompound will be converted to a surface bound alumina phase. Thecalcination may be accomplished in an inert atmosphere, such as innitrogen, or in an atmosphere of air or pure oxygen.

The hydrogen ion will be the predominant positively charged ionbalancing the negatively charged aluminum ion created as a result of theconversion of the aluminum compound to a surface bound alumina phase.Calcination will, of course, also liberate any volatile components.Thus, compositions made in organic solvents with organoaluminumcompounds are, in general, heated from ambient temperature to thecalcination temperature under an inert atmosphere so as to avoidoverheating that might result from combustion of volatile organiccomponents prior to switching to air or oxygen once the calcinationtemperature is reached.

In the preferred embodiment of the present invention, an aluminumalkoxide will be used to coat a fumed silica at an aluminum loadingwithin the range from about 0.02 to about 0.2 mg Al/m² SiO₂ surfacearea. In the most preferred embodiment of the present invention,aluminum isopropoxide will be used to coat a fumed silica. In both thepreferred and most preferred embodiments, the aluminum alkoxide will bedissolved in an aromatic solvent, most preferably toluene. In both thepreferred and most preferred embodiments, the aluminum alkoxide will bedissolved in the aromatic solvent at a concentration sufficient toprovide from about 0.4 to about 10.0 grams of aluminum per liter ofsolvent. Fumed silicas are, of course, well known in the prior art andare available commercially. One such fumed silica, which is particularlyuseful in the catalyst of the present invention, is available from CabotCorporation under the trademark Cab-O-Sil. This particular fumed silica,an average, has a primary particle size within the range from about 70to about 240 Angstroms and a surface area generally within the rangefrom about 90 to about 380 m² /g. In both the preferred and mostpreferred embodiments, from about 10 to about 20 milliliters of aluminumalkoxide solution will be combined with each gram of fumed silica andafter contacting, the aromatic solvent will be distilled off at atemperature within the range from about 30° C. to about 90° C. at areduced pressure within the range from about 380 to about 1 mmHg. Afterthe solvent has been distilled off, the aluminum coated silica will beheated in a vacuum oven at a temperature within the range from about 90°C. to about 300° C., preferably no more than about 200° C. for a timewithin the range from about 12 to about 20 hours, and then calcined at atemperature within the range from about 400° C. to about 900° C.Calcining within this temperature range will result in the production ofacid sites, which are, apparently, more active than acid sites producedat temperatures outside this temperature range. The aluminum coatedsilica will be held at the calcining conditions for a nominal holdingtime within the range from about 15 to 600 minutes, more preferably 60to 240 minutes. In both the preferred and most preferred embodiments,the alumina-on-silica will contain from about 4 to about 200 milligramsof aluminum per gram of fumed silica.

The matrix material used in the preparation of the catalysts of thisinvention can be either inert or active. It is preferred that the matrixmaterial be an inorganic oxide. Inorganic oxide materials suitable foruse herein include amorphous catalytic inorganic oxides, such as silica,alumina, silica-alumina, silica-zirconia, silica-magnesia,alumina-boria, alumina-titania and the like and mixtures thereof.Preferably, the inorganic oxide matrix is selected from alumina, silicaand silica-alumina. By silica-alumina we mean a mixture of alumina andsilica and not the alumina-on-silica additive of this invention. Thesematerials, which are exclusive of the alumina-on-silica component, aregenerally prepared as a cogel of silica and alumina or as aluminaprecipitated on a preformed and preaged hydrogel. In general, the silicais present as a major component in the catalytic solids present in saidgels, being present in amounts ranging from about 55 to 100 weightpercent; preferably from about 70 to about 90 weight percent.Particularly preferred are two cogels, one comprising about 75 weightpercent silica and 25 weight percent alumina and the other comprisingabout 87 weight percent silica and 13 weight percent alumina. Theinorganic oxide matrix component may suitably be present in the catalystof the present invention in an amount ranging from about 40 to about 99weight percent, preferably from about 50 to about 80 weight percent,based on the total catalyst. It is also within the scope of thisinvention to incorporate other materials conventionally employed incracking catalysts, such as various other types of zeolites, clays,carbon monoxide oxidation promoters, etc.

Zeolites which are suitable for use herein are the crystallinealuminosilicate materials having catalytic cracking activity. Suchzeolite materials are described in U.S. Pat. No(s). 3,660,274 and3,944,482, both of which are incorporated herein by reference.Non-limiting examples of such zeolites include both natural andsynthetic zeolites. These zeolites include zeolites of the structuraltypes included in the "Atlas of Zeolite Structural Types" edited by W.M. Meier and D. H. Olson and published in 1978 by the StructureCommission of the International Zeolite Association, which is alsoincorporated herein by reference. Preferred are the faujasites,specifically zeolite X, and zeolite Y. More preferred is zeolite Y, thestructure of which is described in U.S. Pat. No. 3,120,017 which is alsoincorporated herein by reference. More preferred are Calcined Rare EarthY zeolite (CREY) and Ultrastable Y zeolite (USY).

The zeolite may comprise rare earth metal cations and may additionallycomprise hydrogen cations and cations of Group IB to VII metals of thePeriodic Table of Elements. The Periodic Table referred to herein isillustrated in Handbook of Chemistry and Physics, published by theChemical Rubber Company, Clevelend, Ohio, 45th Edition, 1964. Whenadditional cations are present other than rare earth metals and alkalimetals, the preferred additional cations are calcium, magnesium,hydrogen and mixtures thereof. The concentration of hydrogen present inthe finished zeolites will be that concentration equivalent to thedifference between the theoretical cation concentration of theparticular zeolite in question and the amount of cation present in theform of, for example, rare earth and residual ion.

When the rare earth content and alkali metal of the catalyst arecontrolled by utilizing a zeolite which has been treated to comprise atleast a portion of the required rare earth metal, for example, as rareearth metal cations, the zeolite having the desired rare earth metalcomponent can be obtained by various methods.

One method of producing a required zeolite having only a limited amountof rare earth metal cations and low alkali metal content is to startwith a sodium Y-type zeolite and ion exchange it with an ammonium ion bya conventional method known in the art, such as for example, byutilizing an ammonium salt in an aqueous or non-aqueous fluid medium.Ion exchange methods suitable for use herein are described in U.S. Pat.No. 3,140,249; U.S. Pat. No. 3,140,251; U.S. Pat. No. 3,140,253, theteachings of which are hereby incorporated by reference. Although a widevariety of salts can be employed, particular preference is given tochlorides, nitrates, and sulfates. The ion exchange treatment isconducted for a time sufficient to replace enough of the alkali metalcation by ammonium to decrease the alkali metal content of the zeoliteto a desired value. The ammonium treatment may be a single treatment ora successive number of treatments. If desired, the treated zeolite canbe washed between successive ammonium treatments. The resulting ammoniumexchanged zeolite is recovered, for example, by filtration. Therecovered zeolite is washed with water to remove soluble matter. Theammonium exchanged Y zeolite is contacted with a fluid medium comprisingrare earth metal cations of a single rare earth metal or cations of amixture of rare earth metals. The ion exchange is conducted in aconventional way, such as by utilizing salts of the desired rare earthmetals. The rare earth metal treatment additionally replaces some of theremaining alkali metal cations of the zeolite and may replace some ofthe ammonium ions.

The amount of rare earth metal used is such that it does not exceed thelimits of the range required for the catalyst of the present invention.The total amount of required rare earth may be exchanged into thezeolite itself or only a portion of the amount required by the catalystof the present invention may be exchanged into the zeolite and thebalance of the desired required amount may be composited with thefinished catalyst, for example, by post-treating the finished catalystwith a solution comprising rare earth metal components that becomeassociated with the finished catalyst.

The rare earth-exchanged zeolite can be recovered by filtration, andwashed with water to remove soluble matter and calcined, for example, ata temperature ranging from about 1300° F. to 1600° F. for about 0.5 to 6hours, preferably from about 1400° F. to 1500° F. for about 1 to 3 hoursin the absence or in the presence of H₂ O which may be steam or water.

Ultrastable Y-type zeolites are described in U.S. Pat. Reissue No.38,629 (Reissue of U.S. Pat. No. 3,402,996); 4,036,739; and 3,781,199all of which are incorporated herein by reference. In general,"ultrastable" with reference to Y-type zeolite refers to a zeolite whichis resistant to degradation of crystallinity by high temperature andsteam treatment and which has a unit cell size not greater than about24.5 Angstroms and a low alkali metal content. The silica to aluminamole ratio of Ultrastable Y-type zeolite is at least about 3:1.

The final zeolite may be composited with other catalytic metalcomponents, such as metals of Groups IIA, IIIA, IVA, IB, IIB, IIIB, IVB,VIB, and VIII of the Periodic Table of Elements.

The particle size of the zeolite component will generally range fromabout 0.1 to 10 microns, preferably from about 0.5 to 3 microns.Suitable amounts of the zeolite component in the total catalyst willrange from about 1 to 60, preferably from about 1 to 40, more preferablyfrom about 5 to 40, most preferably from about 8 to 35 weight percent,based on the total catalyst.

The catalyst composites of the present invention can be prepared byblending the components in any sequence although it is preferred tostart with the matrix material and blend in the other components. Forexample, if a composite is prepared without the zeolitic material, thenthe alumina-on-silica component is merely blended with the matrixmaterial such that from about 10 to 90 wt. %, preferably about 20 to 70wt. % of the matrix material is present. If the matrix material is asilica-alumina material, then it is preferred to react sodium silicatewith a solution of aluminum sulfate to form a silica-alumina hydrogelslurry which is then aged to give the desired pore properties, filteredto remove extraneous sodium and sulfate ions and then reslurried inwater.

The resulting mixture, or slurry, is then spray dried to produce driedsolids. The dried solids are subsequently reslurried in water and washedsubstantially free of undesired soluble salts. The catalyst is thendried to a residual water content of less than about 15 wt. % andrecovered.

Any conventional FCC process conditions may be used in the practice ofthe present invention. Typical catalytic cracking conditions include atemperature ranging from about 750 to 1300° F., a pressure ranging fromabout 0 to about 150 psig, typically from about 0 to about 45 psig.Suitable catalyst to oil weight ratios in the cracking zone used toconvert the feed to lower boiling products are not more than about 20:1,and may range from about 20:1 to 2:1, preferably from 4:1 to 9:1. Thecatalytic cracking process may be carried out in a fixed bed, movingbed, ebullated bed, slurry, transfer line (dispersed phase) or fluidizedbed operation. Suitable regeneration temperatures include a temperatureranging from about 1100 to about 1500° F., and a pressure ranging fromabout 0 to about 150 psig. The oxidizing agent used to contact thepartially deactivated (i.e., coked) catalyst will generally be anoxygen-containing gas such as air, oxygen and mixtures thereof. Thepartially deactivated (coked) catalyst is contacted with the oxidizingagent for a time sufficient to remove, by combustion, at least a portionof the carbonaceous deposit and thereby regenerate the catalyst in aconventional manner known in the art.

Suitable hydrocarbonaceous feeds for the catalytic cracking process ofthe present invention include naphtha, hydrocarbonaceous oils boiling inthe range of about 430° F. to about 1050° F., such as gas oil; heavyhydrocarbonaceous oils comprising materials boiling above 1050° F.;heavy and reduced petroleum crude oil; petroleum atmosphericdistillation bottoms; petroleum vacuum distillation bottoms; pitch,asphalt, bitumen, other heavy hydrocarbon residues; tar sand oils; shaleoil; liquid products derived from coal liquefaction processes, andmixtures thereof.

Having thus described the present invention and a preferred and mostpreferred embodiment thereof, it is believed that the same will becomeeven more apparent by reference to the following examples. It will beappreciated, however, that the examples are presented for illustrativepurposes and should not be construed as limiting the invention.

EXAMPLES

Catalysts of this invention and comparative catalysts were tested forcracking activity in a standard microactivity test (MAT) as described inthe Oil and Gas Journal, 1966 Vol. 64, pages 7, 84, 85 and Nov. 22,1971, pages 60-68.

EXAMPLE 1

In this example, an alumina-on-silica material was prepared by firstcoating a fumed silica (Cab-O-Sil, M-5 grade) with a toluene solution ofaluminum isopropoxide and thereafter evaporating the toluene and thencalcining the coated silica. The material was prepared by placing 48.8 gof dried silica, 11.08 g of aluminum isopropoxide, and 1000 ml driedtoluene in a 2000 ml round bottom flask. The resulting mixture was thenheated to 40° C. initially at reduced pressure to distill off the bulkof the solvent, and then to 80° C. to distill off the residual solvent.The relatively dry solid was heated overnight in a nitrogen purgedvacuum oven at 100° C. and reduced pressure. The material was placed ina programmable furnace at ambient temperature and heated to 800° C.under nitrogen, then held at 800° C. for 60 min under air. Both nitrogenand air were used at ambient pressure. During heating and calcination,the aluminum isopropoxide became attached to the silica surface(aluminum isopropoxide normally sublimes at 100° C. under reducedpressure) and thermally decomposed to a surface bound alumina phase withliberation of the hydrocarbyl groups of the aluminum isopropoxide. Theresulting material contained 2.8 wt. % aluminum, 42.1 wt. % silicon, and0.04 wt. % carbon. The fumed silica used in preparing this material wasreported by the manufacturer to have a primary particle size of about140 angstroms and a surface area of about 200 m² /g. The resultingalumina-on-silica material is referred to herein as Additive #1.

EXAMPLE 2

Another alumina-on-silica material was prepared as in Example 1 aboveexcept that 49.5 g of dried silica and 37.06 g of alumina isopropoxidewere used. The resulting material, referred to herein as Additive #2,contained 9.34 wt. % aluminum, 40.4 wt. % silicon, and less than 0.01wt. % carbon. The material of this example had a surface area of 197 m²/g.

EXAMPLE 3

In this example, another alumina-on-silica material was prepared byfirst coating a silica gel (Davison) with a toluene solution of aluminumisopropoxide and thereafter evaporating the toluene and then calciningthe coated silica. The material was prepared by placing 53.4 g of driedsilica, 14.22 g of aluminum isopropoxide, and 1000 ml dried toluene in a2000 ml round bottom flask. The resulting mixture was then heated to40-50° C. initially at reduced pressure to distill off the bulk of thesolvent, and then to 90° C. to distill off the residual solvent. Therelatively dry solid was heated overnight in a nitrogen purged vacuumoven at 100° C. and reduced pressure. The material was placed in aprogrammable furnace at ambient pressure and heated to 400° C. undernitrogen, held for 15 min under nitrogen, then held at 400° C. for 60min under air. Both nitrogen and air were used at ambient pressure.During heating and calcination, the aluminum isopropoxide becameattached to the silica surface (aluminum isopropoxide normally sublimesat 100° C. under reduced pressure) and thermally decomposed to a surfacebound alumina phase with liberation of the hydrocarbyl groups of thealuminum isopropoxide. The resulting material, referred to herein asAdditive #3, contained 3.71 wt. % aluminum and 40.55 wt. % silicon. Thesilica used in preparing this material was reported by the manufacturerto have surface area of about 370 m² /g.

EXAMPLE 4

An alumina-on-silica material was prepared in accordance with theprocedure set forth in Example 3 above except that 50.0 g of driedsilica and 28.49 g of aluminum isopropoxide were used. The resultingmaterial, referred to herein as Additive #4, contained 6.22 wt. %aluminum and 38.33 wt. % silicon.

EXAMPLE 5

An alumina-on-silica material was prepared in accordance with theprocedure set forth in Example 3 above except that 55.1 g of driedsilica and 46.34 g of aluminum isopropoxide were used. The resultingmaterial, referred to herein as Additive #5, contained 8.87 wt. %aluminum and 36.16 wt. % silicon.

EXAMPLE 6

A reference Catalyst "A", not a catalyst of this invention, and twocatalysts of this invention, "B" and "C", were prepared by the followingmethod. USY zeolite (LZY-82 from Union Carbide) and thealumina-on-silica additives, as indicated in Table I below, were mixedinto an amorphous silica-alumina gel. The mixture was then driedovernight at 250° F. The dried catalyst was then crushed to 150 mesh andwashed three times with a 5% solution of (NH₄)₂ SO₄. Following thewashing the catalysts were dried overnight at 250° F. and calcined for 3hours at 800° F. The finished catalysts were then steamed at 1400° F.for 16 hours under 1 atmosphere of steam pressure to simulatedeactivation and equilibration in a commercial FCC regenerator. Thesecatalysts were then evaluated using the MAT test for FCC catalysts aspreviously described.

                  TABLE I                                                         ______________________________________                                        Catalyst     A           B        C                                           ______________________________________                                        Composition                                                                   Zeolite, Wt. %                                                                             20 USY,     20 USY,  20 USY,                                     Matrix, Wt. %                                                                              80          60       60                                                       Silica-     Silica-  Silica-                                                  Alumina     Alumina  Alumina                                     Additive, Wt. %                                                                            0           20 #1    20 #2                                       MAT Results                                                                   Conversion                                                                    Wt. % 400° F.                                                                       55          55       57                                          Wt. % 650° F.                                                                       74          75       74                                          H.sub.2 Yield, Wt. %                                                                       0.02        0.02     0.02                                        C Yield, Wt. %                                                                             1.25        1.03     1.22                                        ______________________________________                                    

The above table shows that replacing part of the silica-alumina gelmatrix with alumina-on-silica additive results in better conversion/cokeyield selectivity in both cases.

For the catalyst prepared with Additive #1 containing 2.8 wt. % Al, cokeyield was reduced while conversion to 400° F. products remainedconstant. For the catalyst prepared with Additive #2 containing 9.3 wt.% Al, conversion increased without an increase in coke yield.

Conversion to 650° F. products was also increased or remained constantas the silica-alumina gel matrix was replaced with alumina-on-silicaadditive.

These results are particularly noteworthy because the alumina-on-silicaadditives contain substantially less alumina (i.e., fewer crackingsites) than silica-alumina gel.

EXAMPLE 7

Catalysts D, E, and F, all catalysts of this invention, were prepared ina similar fashion as the catalysts described in Example 6, but usingdifferent alumina-on-silica additives. These catalysts were thenevaluated using a MAT test for FCC catalysts.

                  TABLE II                                                        ______________________________________                                        Catalyst     D           E        F                                           ______________________________________                                        Composition                                                                   Zeolite, Wt. %                                                                             20 USY,     20 USY,  20 USY,                                     Matrix, Wt. %                                                                              60          60       60                                                       Silica-     Silica-  Silica-                                                  Alumina     Alumina  Alumina                                     Additive, Wt. %                                                                            20 #3       20 #4    20 #5                                       MAT Results                                                                   Conversion                                                                    Wt. % 400° F.                                                                       57          57       56                                          Wt. % 650° F.                                                                       77          77       75                                          H.sub.2 Yield, Wt. %                                                                       0.02        0.02     0.02                                        C Yield, Wt. %                                                                             1.25        1.05     1.23                                        ______________________________________                                    

The above table shows that replacing a portion of the silica-aluminamatrix with an alumina-on-silica additive results in higher conversionsto 400° F. and 640° F. products with no increase coke yields.

Coke yields were lowest for Catalyst E, containing Additive #4, a poroussilica gel coated with 6.2 wt. % alumina. This appears to have been theoptimum Al level for this alumina-on-silica because higher Al loadingsof Additive #5, contained in Catalyst F, show reduced conversion whileincreasing coke yields.

EXAMPLE 8

Catalysts G and H were prepared in a similar fashion as the catalystsdescribed in Example 6, but did not contain a zeolite component.Catalyst G is a reference catalyst and Catalyst H is a catalyst of thisinvention. These catalysts were then evaluated using a MAT test for FCCcatalysts.

                  TABLE III                                                       ______________________________________                                        Catalyst    G             H                                                   ______________________________________                                        Composition                                                                   Zeolite, Wt. %                                                                            None          None                                                Matrix, Wt. %                                                                             100 Silica-Alumina                                                                          80 Silica-Alumina                                   Additive, Wt. %                                                                           None          20 #1                                               MAT Results                                                                   Conversion                                                                    Wt. % 400° F.                                                                      40            40                                                  Wt. % 650° F.                                                                      66            66                                                  H.sub.2 Yield, Wt. %                                                                      0.02          0.02                                                C Yield, Wt. %                                                                            1.22          1.15                                                ______________________________________                                    

The table shows that incorporating 20 wt. % of Additive #1 in a silicaalumina gel matrix results in lower coke yield at the same conversion to400° F. and 640° F. products.

This is particularly noteworthy because the alumina-on-silica containsless alumina (i.e., fewer cracking sites) than silica-alumina gel.

EXAMPLE 9

Catalysts I and J were prepared in a similar fashion as the catalystsdescribed in Example 6, but were prepared with a silica gel rather thana silica-alumina gel matrix. In addition these catalysts did not containa zeolite component. Catalyst I is a reference catalyst and Catalyst Jis a catalyst of this invention. These catalysts were then evaluatedusing a MAT test for FCC catalysts.

                  TABLE IV                                                        ______________________________________                                        Catalyst         I        J                                                   ______________________________________                                        Composition                                                                   Zeolite, Wt. %   None     None                                                Matrix, Wt. %    100 Silica                                                                             80 Silica                                           Additive, Wt. %  None     20 #1                                               MAT Results                                                                   Conversion                                                                    Wt. % 400° F.                                                                            4       10                                                  Wt. % 650° F.                                                                           22       30                                                  H.sub.2 Yield, Wt. %                                                                           0.002    0.002                                               C Yield, Wt. %   0.36     0.52                                                ______________________________________                                    

The above table shows that incorporating 20 wt. % of Additive #1 in an"inert" silica gel matrix results in increased conversion to 400° F. and640° F. products, with only a small increase in coke yield.

EXAMPLE 10

A reference Catalyst K, not a catalyst of this invention, and a catalystof this invention, L, were prepared in a similar fashion as thecatalysts described in Example 6, but using a silica gel matrix. Thesecatalysts were then evaluated using the MAT test for FCC catalysts.

                  TABLE V                                                         ______________________________________                                        Catalyst         K        L                                                   ______________________________________                                        Composition                                                                   Zeolite, Wt. %   20 USY   20 USY                                              Matrix, Wt. %    80 Silica                                                                              60 Silica                                           Additive, Wt. %  None     20 #1                                               MAT Results                                                                   Conversion                                                                    Wt. % 400° F.                                                                           42       45                                                  Wt. % 650° F.                                                                           67       71                                                  H.sub.2 Yield, Wt. %                                                                           0.025    0.016                                               C Yield, Wt. %   0.95     1.08                                                ______________________________________                                    

The above table shows replacing a portion of a silica gel matrix withAdditive #1, in a USY zeolite containing composite catalyst, results inhigher conversion to 400° F. and 640° F. products, with only a smallincrease in coke yield.

EXAMPLE 11

A reference Catalyst M, not a catalyst of this invention, and a catalystof this invention, N, were prepared in a similar fashion as thecatalysts described in Example 6, but using a silica gel matrix and aCREY zeolite from Davison. These catalysts were then evaluated using theMAT test for FCC catalysts.

                  TABLE VI                                                        ______________________________________                                        Catalyst        M         N                                                   ______________________________________                                        Composition                                                                   Zeolite, Wt. %  20 CREY   20 CREY                                             Matrix, Wt. %   80 Silica 60 Silica                                           Additive, Wt. % None      20 #1                                               MAT Results                                                                   Conversion                                                                    Wt. % 400° F.                                                                          46        66                                                  Wt. % 650° F.                                                                          67        89                                                  H.sub.2 Yield, Wt. %                                                                          0.006     0.007                                               C Yield, Wt. %  1.79      2.17                                                ______________________________________                                    

The above table shows replacing a portion of a silica gel matrix withAdditive #1, in a CREY zeolite containing composite catalyst, results insubstantially higher conversion to 400° F. and 640° F. products, withonly a small increase in coke yield.

COMPARATIVE EXAMPLE AND EXAMPLE 12

In this example, two alumina-on-silica samples were prepared by firstcoating a fumed silica (Cab-O-Sil, M-5 grade) with a toluene solution ofaluminum isopropoxide, thereafter evaporating the toluene, and thencalcining the alumina coated silica. Each of the samples was prepared byplacing 51 g. of dried silica, 11.58 g. of aluminum isopropoxide, and1000 ml dried toluene in a 2000 ml round bottom flask. The toluene wasthen removed at reduced pressure. Each sample was placed in aprogrammable furnace at ambient temperature and heated to 800° C. undernitrogen, then held at 800° C. for 60 mins. under air. Prior to thisheat treatment, Sample B was subjected to a heat soak at 100° C.overnight (about 16 hours). Both nitrogen and air were used at ambientpressure. During preparation of this Sample B, the aluminum isopropoxidebecame attached to the silica surface (aluminum isopropoxide normallysublimes) and thermally decomposed to a surface bound alumina phase withliberation of the hydrocarbyl groups of the aluminum isopropoxide. Bothof samples A, which represent the Comparative Example, contained 3.24wt. % aluminum, and Sample B contained 3.29 wt. % aluminum. The fumedsilica used in preparing these samples were reported by the manufacturerto have a primary particle size of about 140 angstroms and a surfacearea of about 200 m² /g. The resulting alumina-on-silica material ofSamples A had a measured surface area of 195 m² /g. The resultingalumina-on-silica material of Samples A had a measured surface area of195 m² /g, which is substantially the same as the starting fumed silicamaterial. The surface area of the resulting alumina-on-silica materialfor Sample B was not measured, but it is expected to also besubstantially the same as the fumed silica material.

Each sample (two runs were made with Sample A) was evaluated bymeasuring conversion of the model compound cumene to primarily benzeneand dipropylbenzenes. The evaluation was carried out in a batch reactorunder autogenous cumene pressure at conditions of 650° F. for 60 minuteswith agitation. The results obtained are shown in the table below.

    ______________________________________                                        Sample Al Content                                                                              PPM Al on Cumene                                                                            Cumene Conversion                              ______________________________________                                        A      3.24      303           5.5                                            (Run 1)                                                                       A      3.24      308           3.7                                            (Run 2)                                                                       B      3.29      297           38.0                                           ______________________________________                                    

The above table illustrates the importance of subjecting thealumina-on-silica material of the instant invention to a heat soak priorto calcination. As is evidenced in the table, the conversion activityfor the sample which was subjected to a heat soak is substantiallygreater than the one that was not.

What is claimed is:
 1. A fluid catalytic cracking process whichcomprises contacting, at fluid catalytic cracking conditions, ahydrocarbonaceous feed with a catalyst composite comprised of analumina-on-silica material, which material is comprised of silicaparticles with surface bound aluminum groups chemically bonded to thesilica surface through surface oxygen atoms, which material is dispersedin a matrix comprised of a refractory oxide, and wherein said materialis prepared by: (i) coating silica particles with an aluminum compoundcapable of being thermally converted to an alumina surface phase underthe conditions of (ii) and (iii) hereof; (ii) treating the coated silicamaterial of (i) to a heat soak at a temperature from about 90° C. toabout 300° C. for a period lasting from about 12 hours to about 20 hoursand (iii) calcining the alumina coated silica material to form analumina bound surface phase.
 2. The process of claim 1 wherein the fluidcatalytic cracking conditions include a temperature from about 740° F.to about 1300° F. and a pressure from about 0 to 45 psig.
 3. The processof claim 2 wherein the silica of the alumina-on-silica material has aprimary particle size within the range from about 10 Angstroms to about1000 Angstroms, a maximum aggregate dimension in any direction withinthe range of about 0.01 microns to about 100 microns and a surface areawithin the range from about 1 m² /g to about 2000 m² /g, and wherein thematerial is calcined at a temperature from about 300° C. to about 1000°C.
 4. The process of claim 3 wherein the silica of the alumina-on-silicamaterial is selected from the group consisting of fumed silica, aprecipitated silica, a silica gel, and colloidal silica.
 5. The processof claim 4 wherein the silica is a fumed silica or a silica gel.
 6. Theprocess of claim 1 wherein the matrix is selected from alumina, silicaand a silica-alumina.
 7. The process of claim 5 wherein the matrixselected from alumina, silica and silica-alumina.
 8. The process ofclaim 1 wherein said alumina is coated onto said silica such that saidalumina-on-silica material is comprised of about 0.01 to about 20% wt. %aluminum.
 9. The process of claim 7 wherein said alumina is coated ontosaid silica such that said alumina-on-silica material is comprised ofabout 0.01 to about 20 wt. % aluminum.
 10. The process of claim 1wherein the weight percent of the alumina-on-silica component is about10 to 90 based on the total weight of the composite.
 11. The process ofclaim 9 wherein the weight percent of the alumina-on-silica component tomatrix component is about 10 to
 90. 12. The process of claim 1 wherein azeolite material is also present.
 13. The process of claim 11 wherein azeolite material is also present.
 14. The process of claim 1 wherein thezeolite material is a faujasite.
 15. The process of claim 13 wherein thezeolite material is a faujasite.
 16. The process of claim 15 wherein thefaujasite material is a Y zeolite selected from rare earth Y andultrastable Y.